1. Field of the Invention
The invention relates to a semiconductor device, and more particularly, to a semiconductor device in which different types of semiconductor elements are provided on a single semiconductor layer.
2. Description of Related Art
In recent years, semiconductor devices in which a semiconductor element for switching and a semiconductor device for freewheeling current are provided on a single semiconductor layer have been developed. For example, an inverter circuit that converts direct current (DC) power to alternating current (AC) power is formed by connecting a plurality of these types of semiconductor devices together.
Japanese Patent Application Publication No. 2005-64472 (JP-A-2005-64472) describes one example of a semiconductor device used in an inverter circuit. In this semiconductor device, a Lateral IGBT (Lateral Insulated Gate Bipolar Transistor; hereinafter referred to as “LIGBT”) and a Free Wheeling Diode (hereinafter referred to as “FWD”) are provided on a single Semiconductor on Insulator (SOI) substrate.
FIGS. 11 and 12 are views of the general structure of the semiconductor device described in JP-A-2005-64472. FIG. 11 is a plan layout of the semiconductor device, and FIG. 12 is a sectional view taken along line XI-XI in FIG. 11. As shown in FIGS. 11 and 12, a trench insulation separating portion is provided on a semiconductor layer of the SOI substrate. A portion of the semiconductor layer is divided into two element regions by this trench insulation separating portion. The LIGBT is arranged in one element region, and the FWD is arranged in the other element region.
As shown in FIG. 11, the LIGBT has a structure in which an emitter electrode makes a loop around the outside of a collector electrode in order to reduce the mounting area. Similarly, the FWD also has a structure in which an anode electrode makes a loop around the outside of a cathode electrode in order to reduce the mounting area.
As shown in FIG. 12, a portion of a connecting wire that connects the collector electrode of the LIGBT to the cathode electrode of the FWD is arranged extending laterally above an n−-type voltage-resistance maintaining region (also referred to as a “drift region”) of the LIGBT and the FWD. Normally, high voltage is applied to the connecting wire that connects the collector electrode to the cathode electrode. Therefore, if this connecting wire is arranged above the voltage-resistance maintaining region, electrons will be induced by the electrical potential of this connecting wire, such that the electron concentration will increase at the surface of this voltage-resistance maintaining portion, and the charge of the voltage-resistance maintaining region will become unbalanced. As a result, the electrical potential distribution of the voltage-resistance region will become uneven, suppressing the depletion layer from extending or expanding during reverse bias, so the voltage resistance will end up decreasing.
In order to solve the problem of the voltage-resistance decreasing due to the connecting wire, the applicant of this application proposed the technology described below in Japanese Patent Application No. 2009-209987 (JP-A-2009-209987).
FIG. 13 is a plan layout view of an example embodiment of a semiconductor device according to JP-A-2009-209987, FIG. 14 is a view of the plan layout of the electrodes of the LIGBT and the FWD shown in FIG. 13.
As shown in FIG. 13, a first trench insulation separating portion 120 makes a loop in a quadrangular shape when a SOI substrate 2000 is viewed from above. A second trench insulation separating portion 140 is provided at a distance from the first trench insulation separating portion 120, and makes a loop in a quadrangular shape around the outside of the first trench insulation separating portion 120 when the SOI substrate 2000 is viewed from above. The first trench insulation separating portion 120 and the second trench insulation separating portion 140 extend parallel to each other, with the exception of at the corners, so the space between the two is constant.
Element regions 160 and 180 sandwiched between the first trench insulation separating portion 120 and the second trench insulation separating portion 140 are adjacent to each other at adjacent portions 110 when the SOI substrate 2000 is viewed from above.
The LIGBT is arranged in the first element region 160, and the FWD is arranged in the second element region 180.
In this semiconductor device, a collector electrode 420 of the LIGBT and a cathode electrode 1420 of the FWD (see FIG. 14) are integrally formed as a single common electrode by being connected together. Therefore, a connecting wire that connects the collector electrode 420 to the cathode electrode 1420 is unnecessary. Furthermore, an emitter electrode 480 of the LIGBT and an anode electrode 1480 of the FWD (see FIG. 14) are also integrally formed as a single common electrode by being connected together. Therefore, a connecting wire to connect the emitter electrode 480 to the anode electrode 1480 is also unnecessary. As a result, these connecting wires will not extend above the drift region of the LIGBT and the FWD. Therefore, with this semiconductor device, a situation in which the electrical potential distribution of the drift region becomes uneven will not occur as it does in the related structure shown in FIGS. 11 and 12. Thus, a decrease in voltage resistance due to connecting wires will not occur in this semiconductor device.
However, there are certain problems with this semiconductor device, which will be described below That is, the LIGBT and the FWD are arranged looping around in overall quadrangular shapes when viewed from above, as shown in FIG. 13. If the LIGBT includes the corners (at two locations in the example shown in FIG. 13) of the quadrangular shape, current will concentrate at these corners. That is, at the corners, the area of the collector portion will be smaller than the area of the emitter portion, so current will concentrate at the collector portion, as shown in FIG. 15, reducing the short circuit capacity. FIG. 15 is a view illustrating the way in Which current concentrates at the corners of the LIGBT. Here, the short circuit capacity indicates the time until the semiconductor element fails when high-voltage large-current is applied to a semiconductor element.
Also, as shown in region A encircled by the broken line in FIG. 13, if the region where the LIGBT is continuous is long, the ability of the LIGBT to radiate heat will decrease, so voltage resistance when the element is on will decrease due to the high-temperature LIGBT.